There has been widely used a spark plug including a center electrode, a terminal shell, and a resistor which is provided between the center electrode and the terminal shell for improving the property of preventing generation of radio noise (hereinafter may be referred to as “radio-noise-preventing property”). In such a spark plug including a resistor, a non-metallic electrically conductive material (e.g., carbon) contained in the resistor may be lost through oxidation by electric energy flowing through the resistor, whereby electric resistance may increase, resulting in deterioration of ignition performance (load life performance). Thus, there has been proposed a technique for suppressing an increase in electrical resistance and improving load life performance by incorporating, into a resistor, a Ti (titanium) component such as Ti particles or Ti suboxide particles. See Japanese Patent Application Laid-Open (kokai) No. 2005-327743 (Patent Document 1).
In the case of such a conventional technique (i.e., incorporation of a Ti component into a resistor), when the amount of the Ti component incorporated is large, electric resistance may be greatly reduced during ignition, resulting in deterioration of radio-noise-preventing property. Meanwhile, when the amount of the Ti component incorporated is small, a problem may arise in that load life performance is deteriorated. Thus, the conventional technique (i.e., incorporation of a Ti component into a resistor) is insufficient for improving both load life performance and radio-noise-preventing property; i.e., the conventional technique still has room for improvement.